1. Field of the Invention
This invention relates to a light waveguide lens for use in an integrated optical structure.
2. Description of the Prior Art
As light waveguide lenses, there are known Luneburg lens [R. K. Luneburg: Mathematical Theory of Optics (Univ. of California, Berkeley, 1966) P. 182] in which a mound-like overlay is formed on a light waveguide and the effective refractive index distribution of the light waveguide is endowed with a variation to thereby converge the waveguide light, a geodesic lens [J. Brown: Lens Antennas, Antenna Theory Part 2, ed. R. E. Collin and F. J. Zucker (McGrow-Hill, New York 1969) P. 131] in which a light waveguide is formed on a substrate having a concave portion and the optical path length of the waveguide light is endowed with a variation to thereby cause a converging action to be created, and Fresnel lens [R. Shubert and J. H. Harris: J. Opt. Soc. Am 61 (1971) P. 154] in which the waveguide light is converged by the diffracting action of light. These light waveguide lenses are used as a collimater lens, a Fourier conversion lens [J. T. Boyd and D. B. Anderson: IEEE J, Quantum Electron QE-14 (1978) P. 437] or a condensing lens [Matsumoto, Yamaguchi, Tsuji and Sato: Japanese Laid-open Patent Application No. 111837/1981]. Particularly, where they are used as the Fourier conversion lens or the condensing lens, it is required that the on-axis and off-axis waveguide lights be accurately imaged at a predetermined position
However, in the case of the Luneburg lens, the production accuracy of the refractive index of the overlay formed on the light waveguide is of the order of .+-.0.005 at highest, and this has led to a problem that the focal length differs between products due to the error of the refractive power of each rod made. Also, in other light waveguide lenses such as the geodesic lens and the like, it has been difficult from the viewpoint of the production accuracy to obtain an accurate focal length.
Where the integrated optical structure is used as the head or the like of an optical information processing apparatus, it is necessary to accurately converge light on a fluctuating object surface, and realization of a light waveguide lens which can follow the fluctuation to vary the focal length has been desired.